Process for preventing emulsion formation by acidifying wash water



J. C. PROCESS FOR PREVENTING EMULSION FORMATION June 14., 1960 GEBHART ET AL BY ACIDIFYING WASH WATER Filed Juli) 23, 1956 mmFEz. 9,535 gow mr n Ess nmpxm nz 5% 05:5 o@ N 88E :2; 5.23 :Qi im 30H52 Tm Q @m W N QN NW WN wm. CJ. 5 \N\ Nm W UH. i@ wl l w? i wm Nw uw vm. L MM L Y Wm B n 5.5mm mjtmw 5.5mm wiss ms 95:3 l d NNY* @v un ESE ,5% L f J N Y 9% Tw Nufw l m A n a Q w mmw M625@ Qi ms Q2 @m2 Q S dwf Y Q m mx z\ TQ W\ l Y v Smm Q N NN QN volume.

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United States Patent i' PROCESS FOR PREVENTING EMULSIN FORWA- TION BY ASDIFYING WASH WATER Julius C. Gebhart and Orlin J. Gibbs, Port Arthur, Tex., asslgnors to Gulf Oil Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed July 23, 1956, Ser. No. 599,598

8 Claims. V(Cl. 208-273) This invention relates to stabilization of distillate fuel oils. 1 More particularly, the invention relates to stabilization of fuel oils by acid treatment, neutralization and washing.

It has been found that sulfuric acid treatment of distillate fuel oils that normally tend to darken and/ or deposit sludge during storage will substantially improve the stability of the oils. In order to render the acid treated or sour distillate fuel oils non-corrosive they are neutralized, following acid treatment and separation of acid sludge, with an excess of aqueous alkali. The oil and aqueous alkali phases are separatedv and the neutralized oil is subjected to an aqueous wash. I'he washed oil is Vvtheuseptirated fromthe wash `water'and dried to the extent vdesired to produce a finished oil of improved stability. 'lfhe treated distillate oil can also be redistilled to fxfirther improve its quality, if desired.'

Vv.In the course of stabilizing distillate fuel oils asldescribed above, "it has been found that inadequate washing of the'neutralized oils, causedeither by inadequate ,ad-

mixture of oil and wash water or by the use of insufii` cient wash water, often lresults in reduced stabilityin the finished oils. Attempts to overcome this difficulty inerely by the use of'larger proportions or" water during washing, with vigorous intimate admixture of oil and water, have generally resulted in excessive losses of oil due to emulsiiication. While washing losses can be avoided to some extent, when intimately adrnixing oil and water, by the use of relatively small waterzoil ratios and a large number of Washing stages, or by using a very large volume of wash water and a low degreeof admixture of oil and water, these solutions to the problem are less than fully satisfactory for obvious reasons.

The present invention relates to an improved process for stabilizing distillate fuel oils that normally tend to darken in color and/or to deposit sludge during storage. We have discovered that distillate fuels of good color stability and having reduced sludging tendencies can be produced without excessive Washing losses, without the use of a large number of washing stages, and Without the use of excessive volumes of wash water by the process of this invention. Briefly, this process involves treating a distillate fuel oil that is normally unstable on storage with sulfuric acid of a strength and in a proportion suilicient to improve the storage stability characteristics' of the oil. Sour oil is separated `from acid sludge and neutralized with an aqueous alkali in an amount in excess of that required to neutralize the acidity of the sour oil. Neutralized oilis separated from the aqueous kaliphase and subjected Vto intimateadmixture with-waterthat has Y been acidied with arninor proportion of a strong mineral acid. :The..water:oil proportion isn at least 025:1 by The washed oil is then separated from wash water to produce a distillate fuel oil of improved stability plifieddiowdiagram, of-suitable apparatus in which our process can be practiced. A detailed description of the in the oil.

i 2,940,925 Y lPatented June 14, 1960 distillate oil. Fully satisfactory results have been obtained with 86 percent sulfuric acid, but acid of greater or lesser strength can be used. Normally, good results will be obtained with about to 93 percent sulfuric acid. When treating times and temperatures are sufficiently low, even stronger acid, for example, 98 percent acid and turning sulfuric acidV can be` used. lt is not necessary that the acid be fresh, as excellent results lhave been obtained with partially spent sulfuric acid that has been used in alkylation of olens to 'produce alkylate gasoline. The proportion of acid with respect to the distillate fuel oil will normally vary with the nature of the oil. When reating distillate fuel oils that are very unstable either with respect to color or sludge, such as catalytically cracked distillate oils, it may be necessary touse up to forty pounds or more of acid per barrel of oil'to obtain a high degree of improvement. Conversely, when treatoils that naturally possess fairly good stability characteristics, acid dosages of'as little as 0.5 or 1 pound of acid per barrel can be suicient to effect an improvement For most distillate fuel oils acid dosages of 'about 3 to 30 pounds of acid per .barrel of Aoilwill be found to produce a substantial improvement in stability.

. The acidV treating step is carried'out under. conditions such as to improve the stabilitylof the oil. Normally, acid treating will be carried out at temperatures of between about 60"v and 130 F., 'and at treating times of about 0.25 to aboutl minutes, which temperatures and treating times will depend primarily upon the nature and viscosity of the fuel oil, acid strength, acid:oil proportions, the nature of the `mixing apparatus, and the like.

' acid contacting apparatus marketed by the Stratford Engineering Company is an example of a suitable acid-oil mixing means.

The sulfuric acid reacts with substances in the distillate fuel oil which normallyV act as sludge and dark color precursors and removes them into the oil-immiscible acid phase in the form of acid sludge. vThe acid sludge and any unreacted acid are` then separated omthe acid treated or sour oil, utilizing the inherent irnrniscibility of the acid and acid sludge and the fuel oil and the difference in the densities of the respective phases to effect the separation.. Normally, the quicker the acid sludge is removed from the sour oil, the better the color of the finished oil. Centrlfuging can be employed to obtain rapid sludge separation but good results can also be obtained by gravity settling, especially where the settling vessel is equipped with ballies, packing or the like that are designed to accelerate agglomeration and separation of acid sludge.

Neutralization of the sour oil is elected with aqueous alkali. The aqueous alkali will usually consist of a water solution of caustic soda, but this is not essential, and other aqueous alkaline materials, eg., potassium hydroxide and lithium hydroxide, can be used. The aqueous alkali is used in excess 4of the amount that is requiredto neutralize the acidity of the sour oil. Usually, between about 0.5 and 10 percent by volume of aqueous alkali will be suicient. Y The concentration of the aqueous alkali can vary Widely, for example it can vary ironia' strength equal'to that of lessthan-l to 35 B., i.e.,/about 0.3 to 30 percent, preferably 0.5 to 15 percent, sodium-hydroxide. Neutralization' temperatures between about 60 and 210'F. normally will beused for convenience and/ y of the treating Vequipment at the temperature of the washor in order to minimize the viscosity of the oil, although higher temperatures can be-used in a closed system. The neutralization reaction proceeds rapidly and only the A period of time required for 'thorough intermixtre of sour oil and aqueous alkali must elapse before separation. Again,`suitable contact between sour oil and aqueous alkali can be eected in the conventional, commercial Stratford contacter. o Y K V-After neutralization, the excess of unreacted aqueous falkali, containing dissolved and/or entrained inorganic Y Jsalts, such as sulfates, is separated from the neutralized oil, .utilizing theV immiscibility and different densities of o Y the respective phaseslto etrect separation.` fContinuous Ygravity settling issuitable' for the purposes tofu'this ini; Y After separating the neutralized oilffrom excess aqueous Y alkali, the former is 'subjected to` aprincipal aqueous wash, using wash'Y waterttha-t has been acidied with the minor- 'proportion of a strong mineral acid. The principal wash- Vjing stage is feiected by highly intimate admixture yof wash'Y water and oil. Intimate admixture is accomplished4 by 'vigorous mechanical agitation of oil'and watenwhereby Y Lthe' wash water is reduced to a very small particle or drop- "let size, i.e., small enough that the'water `particles would ordinarily be capable of remaining suspended in the oil,V iorfin otherwords, emulsiable size. This'is done in orderrto approach maximum interfacial contactY between oil. and Water. We have found that ythe desired degree of particlesize' reduction and liquid:liquid interfacial contactl can Ybe obtained byY effectingV adrnixturey ofthe oil andjyvater in a centrifugal pump, but other apparatus ing treatment. By way of illustration, it has been found that about 0.0075 to 0.075 percent, sulfuricY acid based on the weight of the wash water will produce improved results. Equivalent amounts of other acids Will also produce similarly improved results. Washing temperatures will normally-varyrfrom'about 100 to about 210 F.,

in orderitoufacilitatefseparatiorrof oil and water, but lower temperatures can be used, asmca'ne higher temperatures when a `closed system is used. t A f Whilewashing losses ordinarily will be reduced merely by acidifying the wash water used in the principal v-washing stage as indicated above, best results insofar as'stability of the distillate 'ueloils isc'oncerried will be obf tained when the, .proportion of water to oil in the principal washing stage is'at leas't02'5:l by volume, and ordinarily muchV greater, for example, 0.5 :1, 1:1, 2:1 or the like. Ordinarily, ,no additional.v advantage insofar as stability is concerned, willbe obtaiuedbythe, use of greater 'proportions of ,wash ,waterfw 'Auxiliarygwashingf Where the" risk Y of washing lossesis considerably' less severe, can be'satisfactorily' eiected using ,waterzoil vratios Vrif-for example,

excellent results, have Vbeen` obtained using af principal Awashing stage and two subsequent, auxiliary ,water yvaslns,V fthe water used Yinfthe first stage beingaeidiedwtih 0.0.1

percent sulfuric acid, ,wa'tkerzoilV proportionsin: the respective stages'beingjlgl 0.5:'1 audit-1.;

After the neutralized o1lis.,fullywashedlandthe, last @,w'a'sh water-oil separation'is complete, the oilfis preferably dried to remove.stracesjof;fyraten4 Any convenient drying `-desi'gnedto produce 'an Yextremely highv degreeY of intere contactbetween'two normally immiscible liquid phases V1 `,can be used. Bmulsiable'particles are 'usually' consideredV Ytofbe from about 0.001"t.about`lmicron indiameter.

. 'Itbeappreciated that it is by virtue ofthe abovedescribedintimate' admixture of oil and water that adequate Washing can be obtained vwith a relatively small :volume ofV washY water. However, such intimate, adminture tends to promote severe Vemulsiiication difiiculties.

L Normally, best results Will Vbe obtained by first washing the oilin the principal washing stage and then inY one l ormore, preferably two, auxiliary washing stages,`where v ing'reater leeway is permitted in the watenoilproportions landv in the degreeY of admixture. "Where Va/pluralityof washing stages arelemployed, all but theprincipal -Wash can be elfectedwith steam-'condensate condensed in contact with -theoil "instead of Water Vas such. When using fauxiliaryY Washes,iit is not necessary that the waterused :therein be acidiiied, this being essential only -in the prin- VIVcipal' washing stage, sincethe severest washing losses 'and' ".emulsiiication diliculties will Ybe encountered therein. 'However, the water used in auxiliary washing-stages canV be aciditied, if desired, with good results. It is not necessary that theV principal washing stage be placed first in vthe series, when a series of washes is used, provided any preceding Washes are Voperated under'conditions that will Pari/10% salafl,

niean'sean.beused, for examplaairlblowing, obloyii'ng with'andnertfgas suchasnitrogen. Satisfactory sults 'have-been' obtaineduby contactingtheV wetl ioill;rw1tl,1 (1li The present invention is applicable color darkening and/ or sludgeidepos'itioutn storage] For example, rthe'invention is'applicable to'distillate fuel oils Yof the No.` 2 grade that contain .ca 'talytieally'v cracked-fuel oil components, particularly in admixturerowith straight runYV fuel oil distillate,l since such mixturesS normally in- VYvoli/e especially diicult stability problers YAlthough Ithe invention canrbe used inv connection withY straightrunY fuelrfoil distillates, the storage stability problem with suchV oils is ordinarily not severe and.thebenetitsfoftheinvennotV result in emulsitication. Emulsiiication can be avoided stionisrnot limited to the use of sulfuric acid as good re- ,Y

jsultsghaveA also Ybeen obtained withfhydrochloiic acid. Other acidsinclude nitric acidl and phosphorus'f'acids, such "asf phosphorous, and phosphoric l acid.` Theacid should Vtionwill be proportionately limited when treating these oils.- No. 2 fuel oils are dened in the ASTM Standards oniPetroleum Products and Lubricants publishedinNovember, 1954, under designation D396-48T. Y

In a specic embodiment of the invention, with particular reference to the drawing, aY blended No.V 2 distillate fuel oil consisting of 32 percent by volume caustic washed West Texas straight run lfuel oil distillate, 2,8percent by volume Thermofor catalytically cracked light catalytic Ycycle oil, `and 40 percent by volume of fluidcatalytically cracked light cycle oil,V previously -stored in a'jacketed 'vessel (not shown) containing a heat transfer medium in the jacket,- is pumped into the system through linev 2, ,through heat exchanger 4,v in Which'the oil is heated or cooled, as needed,rto the desired cont-acting temperature, for example, -about 90 F.V From Yheat exchanger 4, `the Yoil passes through line 6 into mixing ves-s e118; `Ther-oil is preferably dried before admixture with ltheaeid, as for Vexample byflterin'g through'rock. salt in Yal Vessel,g not shown, similar to iilter V16.- Sulfuric acid,lfvorjexample,

'86 percent vacid recoveredfrom an alkylationfuniggis pumped :from storage, not shown, by.displacenient-with transformer oil, through line 10 vinto mixingwesseltl.

Vessel 8"-can be a' commercial Stratford'contacto'rgorsas n shown,Y a turbo-mixer. Thelat'ter. is equipped: withfa .be 'ernp'aloyedV in'theV wash. Water in Ya.proportiongre'ater Y than'that, required to neutralize any `traces of alkali rethe oil, lbut not kso great as to Vcause corrosion centrally'l positioned shaft having turbo-mixerfrotors fmoimted thereonV Dubo-mixer' s'ttors are positionedat the .sa-me. height 'as the @tors 'sul-uve .Sfatifrisfyz Shaft*- foils. that exhibit a substaritiallfprjt)bleirt'withl respecta'to assegnati The rotor shaft is rotated at, for example, 1G00 r.p.m. The acid dosage is sufficient to etect an improvement in the storage stability characteristics of the oil, for example, 7.5 :0.2 pounds acid per barrel of oil. The oil and acid are contacted in vessel 8 for an average of 50i4 minutes.

The sour oil-acid sludge mixture is removed from vessel 8 via line 12 into vessel 14, line 20 and identical vessel 14', where acid sludge is separated and withdrawn from the system by way of lines 18 and 1S. Vessels 14 andr14' are provided With conical distributing battles and are packed-with approximately 3A inch diameter rock, designated `by numerals 16 and 16', to assist inseparation ofl'sludge from sour oil.

Aqueous caustic soda solution (e.g., 1 percent by weight) is continuously introduced into the system via line 26 and admixed with sour oil from vessel 14 and line 22 in contactor 24 in a proportion more than suicient to neutralize the acidity of the sour oil, for example, 0.li0.02 volume of caustic per volume of sour oil. The neutralization temperature is conveniently the temperature of the sour oil, or in this case about 90i5 F.

The neutralized oil and aqueous caustic phase, containing unreacted caustic, water, and dissolved and eutrained inorganic salts, is directed out of contactor 24, through line 28, through heater 30, into line 32 and thenceinto jacketed caustic settler 34. The oil-caustic mixture is heated in heater 30 to a degree sucient to facilitate separation of the oil and aqueous phases in caustic settler 34. In this embodiment, a temperature of l60il0 F. is used. Caustic settler 34 is provided with a jacket and a heat exchange medium is circulated through the jacket to maintain the desired settling ternperature. Vessel 34, similarly as cone-bottomed water settlers S0, 60 and 70, is provided with inverted conical distributor battles. Settled, partially spent caustic solution is withdrawn from vessel 34 by way of line 38. Neutralized oil is removed from vessel 34 by Way of line 36.

Wash Water that has been aciditied by the addition of a strong acid in an amount more than suicient to neutralize the residual basicity of the oil, for example, 0.01 percent sulfuric acid, is introduced into the principal Washing stage of the system by Way of line 86 and manifold line 90. The acidied Wash water is preheated in heater 88, ordinarily to about the same degree as the oil from caustic settler 34, so as to facilitate separation of oil and wash water. In the present embodiment aciditied wash water is passed through valve 92 into line 46 Where it is intermingled with neutralized oil from line 36. Introduction of acidied wash Water solely into the rst Washing stage is not essential, and if desired acidiied wash water can be introduced into any or all additional Washing stages, by way of valves 94 and 96 in the present embodiment. From line 46, the mixture of acidied Wash water and oil is passed through a centrifugal pump mixer 48 to obtain a high degree of interfacial contact between oil and Wash water and thence through line 46a into water settler 50, which is similarly constructed as caustic settler 34. Wash water containing extracted impurities is settled out of the oil in settler 50 and withdrawn from the system through line 52. Oncewashed and settled oil is passed overhead through line 54. The washed oil is then admixed either with additional acidiied wash water from line 90 and valve 94, or as in the presently described embodiment, with nonacidied wash water which is introduced into the auxiliary washing stages of the system by way of line 40, heater 42, manifold 44 and valve 47. 'Ihe Water from line 40 is preheated to about the same degree as the aciditied wash water. The oil and Water are vigorously admixed in globe valve 56 and the mixture passes into vessel 60 for settling. In the presently described embodiment vessels 60 and 70 and valves 45, 66, 62, 72 and 96 function similarly as their counterparts in the previous stage.

Thethricewashedand settled oilis passed outof-tlie lastsettler 7S) through line 74, into salt lter chamber 76, lledwith "$4 inch to inch rock salt supportedby a 1A inch wire grid. Any entrained Water in the fuel oil is settled outl in the form of salt water in vessel 76, from which it can Ybe drained periodically through line 78. Bright fuel oil having a light color and good stability characteristics is passed overhead through line 80, through cooler 82, and `into line .84 to storage facilities not shown.

Distillatefuel oils obtained as described in the foregoing speciiic embodiment were tested for stability by a standard accelerated stability test. The accelerated storage stability test referred to inthe description of this invention is carried out by heating 600 gram samples of the fuel oil composition being tested for periods varying from 16 to 64 hours at 210 F. in loosely stoppered, one-quartV clear glass bottles. Following each heating periodeach test sample is cooled to room 'temperature and filtered by suction through tared, medium porosity fritted glass Gooch-type crucibles. The sludge in each Crucible is washed with heptane. The respective crucibles are then dried in an oven maintained at 210 F. for one hour, cooled in a desiccator and reweighed. The increase in weight is recorded as milligrams of sludge per 600 grams of oil. The color of the oil ltrates is recorded as ASTM Union color units. Using a rough rule of thumb based on experience, one hour of storage under the conditions of the accelerated test isy equivalent to about ten days of storage under actual eld conditions.

The results of the foregoing runs are presented below together with comparative test results obtained with the untreated No. 2 fuel oil stock and with two similar runs wherein non-aciditled wash water was used.

Table A Run No Charge Run 1 Run 2 Run 3 Stock Washing Conditions:

Water to First Washing Stage:

VOL/Vol Oil l 1 1 0.5 Water to Second Washing Stage VOL/'VOL 0.2 1 1 Water to Third Washing. Stage:

VOL/Vol. Oil 0.5 1 l Yields: Vol. Percent of Charge:

Finished O 98. 5 Emulsion Washing Loss.- (Lg Emulsion l. Inspections:

Stability at 210 F.-

Color, ASTM Union:

Initial Filtrate 1. 75 1. 25 After AginglHrs 4.75 1.5 32 Hrs 1. E 64 Hrs 1. 75 Sludge: MgJSOO G. Oil:

Existent 3 2 After Aging- 16 Hrs 45 2 32 Hrs 5 64 Hrs 7 e Acid Water (0.01% H2501).

Non-acidic water washing in the principal washing stage resulted in such stable emulsions in that Washing stage that the runs could not be continued, and no inspections on the product could be obtained. In contrast acidification of the principal Washing stage in run l enabled the production of light-colored fuel oil distillate that exhibited greatly improved stability characteristics. Similar improved results are obtained when treating other distillate fuel oil blends of the kind disclosed herein with the same or equivalent amounts of other disclosed acids, ywhen Yusing a greater or lesser number of washing stages, when using other herein disclosed Washing proportions, and when using steam instead of water in washing stages other than the principal stage.

When another sample of distillate fuel oil having the same make-up as that in the foregoing table was treated similarly as in the foregoing specific embodiment, but using non-acidied water and water:oil proportions of Y c 7 0.131, 0.2:1 and O.2':1in the respectivewashing stages, in other words insuicient proportions to cause emulsi- :cation and large washing losses under the conditionsvof ,i,e., aboutj 0.25 :l Yor higher, will result in'exce's'sive wash- ,ing'losses, while similarv washing with 'arelatively small 1Vproportionof wash water, ie., less Vthan 0.25 :1, will rei Vsult in poor stability of theoil. However, as demonstrated by Arun, 1 in Table A, intimate Washing of the oil in the principal washing stage with a relatively large proportion of Vacidiiied water, i.e., more than 0.25:l, will producegajriinished oil of good -stability Withoutsevere fwashing losses. Y I

' It/,wilibe understood that many variations'oi foregoing process will occur to those Skilled inthe art, and

1. A process comprising eontactinga'distiHate fuelroil' that is normally unstable during storage with sulfuric Yacid of a strength and in aeproportion suicient to improve the storage Vstability characteristics of the oil, separating acid sludge from ,the 4acid treated oil and neutralizing the latter with anexcess of an aqueous alkali, 'separating the aqueous alkli'phse' from the neutralized oil and subjecting the latterto highly intimateadmixture `with 4washwater that has been acidil'ied With a strong mineral acid in a proportion sutcient to produce an acidity equivalent to 0.0075 to 0.075 percent sulfuric acid, the water:oil proportion Ibeing at least about 0.25: 1, and separating washed oil from wash water to produce a dis-tillate fuel oil of improved storage stability characteristics. f v

2. A process comprising treating a mixture of catalyticallycracked and straight run fueloil distillates that is normally unstable during storage with sulfuric acid of a strength'and in a proportion sucient to improve the 'storage stability Vcharacteristics of the oil, separating acid sludge from sour oil and neutralizingV the latter with an Yexcess of an Aaqueous alkali, separa/ting neutralized oil from the aqueous alkali phase and intimately admixing the Yformer with wash water in the Iform of droplets of emulsifiable size, said wash water beingV -acidied with a strong mineral acid in avproportion suflicient to produce an acidityequivalent @0.0075 to 0.075 percent lsulfuric acid, the water-:oil ratio during said intimate admixingbeing from about 0.25 :l to about 2:1, and separating the washedoil from wash water to produce a distillate fuel oil jof improved storage stability characteristics.

3. A processcomprising treating a distillate fuel oil `that is normallyunstable during storage with 80 percent to fundingY sulfuric acid ina proportion of about.0.5 to

storage stability-characteristics of the oil, separating acidY sludge from sour oil and neutralizing the latter with an excess of an aqueous alkali solution comprising about 0.3 tjo 30 percentlsodium hydroxide, separating neutralized oilfrom'the aqueous alkali Vphase and intimately admixing said neutralized oil with wash water in theform of droplets of emulsiable size, Vsaid Wash water having been acidied with a strong mineral -acid in a proportion Vto produce an acidity equivalent to 0.0().75fto0l75VV percent sulfuric acid, the water:oil ratio Vduring said. intimate admixing being from about 025:1 to about.2:l, and separating-washed oil from wash water to produce a distillate fuel oil of improved storage stability characteristics.

4. TheV process of claim 3 wherein the Washedcilis subshelzquently subjected to at least one auxiliary aqueous was 5.Y A process comprising treating a mixture of catalytically cracked and straight run. fuel oil distillates that is normally unstable during vstorage with to 93 percent sulfuric acid in a proportion of about 3 `to 30 pounds ofacid per rbarrel of oil, theV strength yand proportion of said acid being suicient toY improve the storage stability characteristics .of the oil, separatingacid sludgefrom sour oil and neutralizing the lat-ter with an excess of an `aqueous alkali solution comprising about 0.5 -to 10 percent by volume of anV 0.5 to 15 percent aqueous solu- Ition of Vsodium hydroxide, separating neutralized oil from the aqueous alkali phase andbefore contactingV the-neutralized Voil with water under emulsifying conditions, intimately admixing said neutralized oil with wash water in the form of droplets of emulsiable size, said Wash Water havingbeen acidified with' 0.0075 nto 0.075 percent sulfuric acid, the water:oil ratio during said intimate adbeing from about 0.5:1 to about 2:1, `separat ing the Washed oil from Vwash water, subjecting the washedA oil to at least one auxiliary aqueous Wash and separating washed oil toproduce a distillate fuel oil of improved storage stability characteristics. n

6. The process of claim 5 wherein the waterzoil'ratio 4in said auxiliary wash is 0.1:1 to 2:1. a v

a, 7.,'I'he process of claim 5 wherein the washed oil is 'redistilled to produce a nished oil having improved storage stability characteristics. v

8. A process consisting essentially of contactingadis- Vtillate fueljoil that is normallyV unstable during storage with sulfuric yacid of a strength and in a proportion sutlicientrto improvejathe storage stability characteristics of the oil, separating acid sludge from the acid treated oil and vneutralizing the latter with an `excess of an aqueous alkali, separating the aqueous alkali phase from'the neutralized oil and subjecting the latter to highly intimate Vadrnixture `with wash water that has been aciditi'ed with a lstrong mineral acid in a proportion suiiicient'to produce an acidity equivalent Yto 0.0075 to 0.075 percent sulfuric acid, the Awatenoil proportion being at least about I 0.25:1,.and separating washed oil from wash Awater to producea distillate fuel oilof improved storage stability fcharacteristics. Y

References cited in the me of this patent UNITED STATES PATENTS Y12,315,766 Border Apr.'6, 1943 2,434,528 Wadley i Ian. 13, 1948 52,662,062 Sumerford Dec.'8, 1953 2,729,594 Alderson etal.. Jan. 3, 195.6

" FOREIGN' PATENTS 705,267 Great Britain MarflOj l954 

1. A PROCESS COMPRISING CONTACTING A DISTILLATE FUEL OIL THAT IS NORMALLY UNSTABLE DURING STORAGE WITH SULFURIC ACID OF A STRENGTH AD IN A PROPORTION SUFFICIENT TO IMPROVE THE STORAGE STABILITY CHARACTERISTICS OF THE OIL, SEPASRATING ACID SLUDGE FROM THE ACID TREATED OIL AND NEUTRALIZING THE LATTER WITH AN EXCESS OF AN AQUEOUS ALKALI, SEPARATING THE AQUEOUS ALKALI PHASE FROM THE NEUTRALIZED OIL AND SUBJECTING THE LATTER TO HIGHLY INTIMATE ADMIXTURE WITH WASH WATER THAT HAS BEEN ACIDIFIED WITH A STRONG 